This invention relates to a safety device for a swimming pool heater, and more particularly to a roll-out flame detector for a swimming pool heater.
A swimming pool heater basically includes a combustion chamber, in the lower portion of which are mounted burner tubes. A fluid fuel, such as gas, is supplied to the burner tubes through a control valve mounted on the outside of the fire wall of the combustion chamber. In the upper portion of the combustion chamber are mounted the heat exchanger coils or tubes through which the swimming pool water flows for heating by the flame from the burner tubes. Because of the tremendous volume of water that must be heated in a swimming pool, a great number of heat exchanger coils are spaced close together to provide a maximum amount of surface area exposed to the flame. Accordingly, the close spacing of the heat exchanger coils restricts the passage of the products of combustion, and the coils become coated, and oftentimes clogged with soot from the flames. When the pool heater is inoperative, the coils collect dust from the environment, as well as rust from condensation. Moreover, the orifices in the burner tubes are likely to become clogged with soot, dirt or rust over a period of time, because of the small size of the flame orifices, and because of the same heating and environmental conditions which produce the soot, dust, and rust on the heat exchanger coils.
If either or both of the heat exchanger coils and the burner orifices are sufficiently clogged, the flow of the products of combustion from the combustion chamber will be substantially impeded, forcing the flame from the burner tubes to roll out beneath the fire wall into the control chamber, and expose the control valve not only to overheating, but to rupture, and even opening of the main gas supply pipe, thereby presenting a substantial fire and explosion hazard. Several such accidents have actually occurred resulting in substantial property damage and personal risk.
Heretofore, the only remedy for the above described hazardous situations has been in repeated inspections of the condition of swimming pool heaters, and particularly the condition of the heat exchanger tubes and the burner orifices.
The following U.S. patents disclose various types of safety devices for shutting off the flow of fuel to a burner in a heating system when an overheated condition is detected by a thermal sensing element:
U.S. Pat. No. Re.28,013, McLarty: May 24, 1974 PA0 U.S. Pat. No. 2,776,000, Miller: Jan. 1, 1957 PA0 U.S. Pat. No. 3,469,569, Brockbank: Sept. 30, 1969 PA0 U.S. Pat. No. 3,537,803, Ignazio: Nov. 3, 1970 PA0 U.S. Pat. No. 3,652,195, McIntosh et al: Mar. 28, 1972 PA0 U.S. Pat. No. 4,089,632, Rexroad: May 16, 1978.
All of the thermal sensing elements disclosed in the above patents, except the Ignazio patent, are fusible elements. Moreover, the Rexroad patent recites additional prior patents disclosing fuel controls incorporating fusible elements.
The Rexroad U.S. Pat. No. 4,089,632 discloses an elongated fusible element 30 mounted in a bracket having a non-conducting base on the exterior wall of the combustion chamber of a gas or oil burning appliance, such as a hot water heater, furnace, boiler, or stove. The fusible element is connected in series with the fuel control valve and thermocouple, so that melting of the fusible element will break the electrical control circuit and shut down the fuel control valve.
However, the above patents do not disclose a fusible roll-out flame detector specifically designed and constructed for use in connection with a swimming pool heater, much less the particular construction of the flame fuse detector per se.